install libapt-private* into the apt binary

debian/apt.install

@@ -2,3 +2,4 @@ bin/apt-* usr/bin/
 bin/methods/* usr/lib/apt/methods/
 scripts/dselect/* usr/lib/dpkg/methods/apt/
 usr/share/locale/*/*/apt.mo
+bin/libapt-private* usr/lib/@DEB_HOST_MULTIARCH@/